全文获取类型
收费全文 | 14503篇 |
免费 | 1510篇 |
国内免费 | 4篇 |
出版年
2022年 | 88篇 |
2021年 | 222篇 |
2020年 | 115篇 |
2019年 | 150篇 |
2018年 | 219篇 |
2017年 | 200篇 |
2016年 | 299篇 |
2015年 | 538篇 |
2014年 | 597篇 |
2013年 | 772篇 |
2012年 | 846篇 |
2011年 | 882篇 |
2010年 | 554篇 |
2009年 | 486篇 |
2008年 | 749篇 |
2007年 | 776篇 |
2006年 | 659篇 |
2005年 | 697篇 |
2004年 | 635篇 |
2003年 | 616篇 |
2002年 | 596篇 |
2001年 | 212篇 |
2000年 | 203篇 |
1999年 | 193篇 |
1998年 | 201篇 |
1997年 | 171篇 |
1996年 | 157篇 |
1995年 | 135篇 |
1994年 | 157篇 |
1993年 | 145篇 |
1992年 | 196篇 |
1991年 | 162篇 |
1990年 | 139篇 |
1989年 | 148篇 |
1988年 | 131篇 |
1987年 | 154篇 |
1986年 | 113篇 |
1985年 | 153篇 |
1984年 | 164篇 |
1983年 | 133篇 |
1982年 | 160篇 |
1981年 | 140篇 |
1980年 | 126篇 |
1979年 | 119篇 |
1978年 | 95篇 |
1977年 | 89篇 |
1976年 | 99篇 |
1974年 | 99篇 |
1973年 | 86篇 |
1972年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
1.
2.
Keratinocyte growth-promoting activity from human placenta 总被引:4,自引:0,他引:4
Extracts of term human placenta were tested for enhancement of proliferative growth of primary cultures of human keratinocytes. Saline extracts or supernatants from homogenates were dialyzed extensively, lyophilized, and tested in subcultures of keratinocytes in MCDB 153 medium with 0.1 mM Ca++ containing only defined supplements (insulin, hydrocortisone, transferrin, ethanolamine, phosphoethanolamine). Cells plated in the absence of EGF at moderately high densities (1000-3000 cells per cm2) formed colonies and grew in the presence of placental extract at 25-500 micrograms/ml. Extracts of cord serum or maternal serum were inactive, suggesting that the activity is derived from placental tissue. The activity is not EGF, since the activity in the placental extract, unlike EGF, did not promote growth at low cell density, was synergistic with EGF under some conditions, and did not produce changes in colonial morphology which occurred in the presence of EGF. Unlike keratinocyte growth-promoting activity in bovine hypothalamic extract, the activity is non-dialyzable and is destroyed at 100 degrees C. Placental extract could not replace any of the defined components of the medium and is therefore distinct from them. The presence of activity in the placenta with distinctive properties suggests that this is a previously undescribed material with growth-promoting properties for epithelium. 相似文献
3.
4.
5.
6.
7.
Membrane targeting of RecA during genetic transformation 总被引:2,自引:1,他引:1
H. Robert Masure Barbara J. Pearce Helen Shio & Barbara Spellerberg 《Molecular microbiology》1998,27(4):845-852
Recombination in prokaryotes and eukaryotes is mediated by the RecA family of proteins. Although the interactions between RecA and DNA are well studied, the cellular location of these interactions is not known. Using genetic transformation of Streptococcus pneumoniae as a model system, there was increased expression of a protein, colligrin, and RecA, products of the rec locus during genetic transfer. These proteins formed a complex and were found associated with the membranes of genetically competent cells. With immunoelectron microscopy and subcellular fractionation, we showed that the induction of competence led to the translocation of RecA and colligrin to the membrane and to the formation of clusters of RecA in a colligrin-dependent step. Based on the behaviour of colligrin and RecA during genetic exchange and the numerous proteins in prokaryotes and eukaryotes with domains similar to colligrin, we suggest that there may exist a family of proteins, which gathers macromolecules at specific sites in biological membranes. 相似文献
8.
William Russell 《BMJ (Clinical research ed.)》1985,290(6485):1914
9.
Paul D. Bonnitcha Simon R. Bayly Mark B.M. Theobald Helen M. Betts Jason S. Lewis Jonathan R. Dilworth 《Journal of inorganic biochemistry》2010,104(2):126-9888
Combination agents comprising two different pharmacophores with the same biological target have the potential to show additive or synergistic activity. Bis(thiosemicarbazonato)copper(II) complexes (e.g. 64Cu-ATSM) and nitroimidazoles (e.g. 18F-MISO) are classes of tracer used for the delineation of tumor hypoxia by positron emission tomography (PET). Three nitroimidazole-bis(thiosemicarbazonato)copper(II) conjugates were produced in order to investigate their potential as combination hypoxia imaging agents. Two were derived from the known bifunctional bis(thiosemicarbazone) H2ATSM/A and the third from the new precursor diacetyl-2-(4-N-methyl-3-thiosemicarbazone)-3-(4-N-ethylamino-3-thiosemicarbazone) - H2ATSM/en. Oxygen-dependent uptake studies were performed using the 64Cu radiolabelled complexes in EMT6 carcinoma cells. All the complexes displayed appreciable hypoxia selectivity, with the nitroimidazole conjugates displaying greater selectivity than a simple propyl derivative used as a control. Participation of the nitroimidazole group in the trapping mechanism is indicated by the increased hypoxic uptake of the 2- vs. the 4-substituted 64Cu-ATSM/A derivatives. The 2-nitroimidazole derivative of 64Cu-ATSM/en demonstrated superior hypoxia selectivity to 64Cu-ATSM over the range of oxygen concentrations tested. Biodistribution of the radiolabelled 2-nitroimidazole conjugates was carried out in EMT6 tumor-bearing mice. The complexes showed significantly different uptake trends in comparison to each other and previously studied Cu-ATSM derivatives. Uptake of the Cu-ATSM/en conjugate in non-target organs was considerably lower than for derivatives based on Cu-ATSM/A. 相似文献
10.